The invention relates to turbine engines, and in particular to aeroengines and to industrial turbines, more particularly to turbine nozzles and to compressor diffusers for such turbine engines.
Improving the performance of turbine engines and reducing their polluting emissions has led to envisaging ever higher operating temperatures.
For hot elements in turbine engines, proposals have therefore been made to use ceramic matrix composite (CMC) materials. Such materials possess remarkable thermostructural properties, i.e. mechanical properties that make them suitable for constituting structural elements, together with the ability to conserve those properties at high temperatures. Furthermore, CMC materials are of density that is considerably lower than the density of the metal materials conventionally used for elements in the hot portions of turbine engines.
Thus, documents WO 2010/061140, WO 2010/116066, and WO 2011/080443 describe making turbine engine rotor wheel blades out of CMC, the blades having inner and outer platforms incorporated therein. The use of CMC materials for turbine nozzles has also been proposed, in particular in document WO 2010/146288.
A conventional metal turbine nozzle is made up of a plurality of assembled-together sectors, each sector comprising an inner platform, an outer platform, and a plurality of airfoils extending between the inner and outer platforms and secured thereto. The inner and outer platforms define an annular flow passage for gas through the nozzle. On the inside, it is common practice to provide an abradable material carried by the inner platforms and co-operating with sealing wipers secured to a rotor of the turbine. The abradable material is typically in the form of a honeycomb metal structure.
When the turbine nozzle is made up of CMC sectors, there is a problem of attaching the abradable material.
A similar problem arises in compressor diffusers made up of CMC material sectors supporting an abradable material on the inside of inner platforms.